they look like exactly the same format as the output file, just "cat" them all together from DOS/Unix prompt or you can do same from perl
dos prompt> type *.txt >>outputfilename
unix prompt> cat *.txt >>outputfilename
Perl (dos/unix prompt)> perl -e "{`system cat $_ >>outputfilename`}" *.txt
haven't tested the perl version so you may need do adjust a little.